Method of manufacture of an electrowetting device

ABSTRACT

An apparatus for manufacture of an electrowetting device is provided. The apparatus includes a first and second support plate feeding system to provide a first and second support plate respectively. The first and second support plate feeding systems include a first and second element respectively. The first and second elements are positioned relative to each other so as to angle the first support plate relative to the second support plate such that the first support plate and the second support plate are brought closer together as the first support plate and the second support plate are fed by the first element and the second element, respectively, so as to provide, during the manufacture of the electrowetting device, a cavity between the first support plate and the second support plate. The apparatus also includes a first and second fluid supply system for supply of a first and second fluid respectively.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application of U.S. patent application Ser. No.14/320,129, filed Jun. 30, 2014, the contents of which are incorporatedby reference herein in their entirety.

BACKGROUND

Known methods of manufacturing an electrowetting device can requirelarge volumes of fluid for dispensing a relatively small amount of thefluid for the finally manufactured device. This can lead toinefficiencies in manufacture, for example wasting of unused volumes offluid which can be expensive and high rates of evaporation of fluidsbeing dispensed.

It is desirable to provide a more efficient method of fluid dispensingfor manufacture of an electrowetting device.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows schematically an example display element;

FIG. 2 shows a plan view of the example display element;

FIGS. 3 to 6 each show different examples of a part of a method ofmanufacturing an electrowetting device; and

FIGS. 7 and 8 show flow diagrams of examples of a method ofmanufacturing an electrowetting device.

DETAILED DESCRIPTION

FIG. 1 shows a diagrammatic cross-section of part of an example of anelectrowetting display device 1, including a plurality of pictureelements or display elements 2, one of which is shown in the FIG. andwhich may also be referred to as an electrowetting cell. The lateralextent of the display element is indicated in the FIG. by two dashedlines 3, 4. The display elements comprise a first support plate 5 and asecond support plate 6. The support plates may be separate parts of eachdisplay element, but the support plates may be shared in common by theplurality of display elements. The support plates may include a glass orpolymer substrate 6, 7 and may be rigid or flexible. In manufacturingexamples described below the substrate is sufficiently flexible,transparent and may be formed for example of polycarbonate orpolyethylene naphthalate (PEN), “polyester 12,13” or poly (ethyleneterephthalate), or any other suitable material as the skilled personwill appreciate.

The display device has a viewing side 8 on which an image or displayformed by the display device can be viewed and a rear side 9. In theFIG. a surface of the first support plate 5, which surface is in thisexample a surface of the substrate 7, defines the rear side 9; a surfaceof the second support plate 6, which surface is in this example asurface of the substrate 6, defines the viewing side; alternatively, inother examples, a surface of the first support plate may define theviewing side. The display device may be of the reflective, transmissiveor transflective type. The display device may be an active matrix drivendisplay device. The plurality of display elements may be monochrome. Fora color display device the display elements may be divided in groups,each group having a different color; alternatively, an individualdisplay element may be able to show different colors.

A space 10 of each display element between the support plates is filledwith two fluids: a first fluid 11 and a second fluid 12 at least one ofwhich may be a liquid. The second fluid is immiscible with the firstfluid. Therefore, the first fluid and the second fluid do notsubstantially mix with each other and in some examples do not mix witheach other to any degree. The immiscibility of the first and secondfluids is due to the properties of the first and second fluids, forexample their chemical compositions; the first and second fluids tend toremain separated from each other, therefore tending not to mix togetherto form a homogeneous mixture of the first and second fluids. Due tothis immiscibility, the first and second fluids meet each other at aninterface which defines a boundary between the volume of the first fluidand the volume of the second fluid; this interface or boundary may bereferred to as a meniscus and is shown in FIG. 1 as an interface 57 withfirst fluid contracted with a voltage applied and as an interface 55when a zero voltage is applied. With the first and second fluidssubstantially not mixing with each other, it is envisaged in someexamples that there may be some degree of mixing of the first and secondfluids, but that this is considered negligible in that the majority ofthe volume of first fluid is not mixed with the majority of the volumeof the second fluid.

The second fluid is electrically conductive or polar and may be water,or a salt solution such as a solution of potassium chloride in water.The second fluid may be transparent; it may instead be colored orabsorbing. The first fluid is electrically non-conductive and may forinstance be an alkane like hexadecane or may be an oil such as siliconeoil.

The first fluid may absorb at least a part of the optical spectrum. Thefirst fluid may be transmissive for a part of the optical spectrum,forming a color filter. For this purpose the first fluid may be coloredby addition of pigment particles or a dye. Alternatively, the firstfluid may be black, i.e. absorb substantially all parts of the opticalspectrum, or reflecting. A reflective first fluid may reflect the entirevisible spectrum, making the layer appear white, or part of it, makingit have a color. In examples to be described below, the first fluid isblack and therefore absorbs substantially all parts of the opticalspectrum, for example in the visible light spectrum. The term“substantially absorbs” includes a degree of variation, therefore thefirst fluid may not absorb all wavelengths, but the majority ofwavelengths within a given spectrum such as the visible spectrum, so asto perform the function of the first fluid in the element. The firstfluid is therefore configured to absorb substantially all light incidenton the first fluid. For example the first fluid may absorb 90% or moreof light in the visible spectrum and incident on the first fluid. Thesupport plate 5 includes an insulating layer 13. The insulating layermay be transparent or reflective. The insulating layer 13 may extendbetween walls of a display element. To avoid short circuits between thesecond fluid 12 and electrodes arranged under the insulating layer,layers of the insulating layer may extend uninterrupted over a pluralityof display elements 2, as shown in the FIG. The insulating layer has asurface 14 facing the space 10 of the display element 2. In this examplethe surface 14 is hydrophobic. The thickness of the insulating layer maybe less than 2 micrometers and may be less than 1 micrometer.

The insulating layer may be a hydrophobic layer; alternatively, it mayinclude a hydrophobic layer 15 and a barrier layer 16 with predetermineddielectric properties, the hydrophobic layer 15 facing the space 10, asshown in the FIG. The hydrophobic layer is schematically illustrated inFIG. 1 and may be formed of Teflon® AF1600. The barrier layer 16 mayhave a thickness, taken in a direction perpendicular the plane of thesubstrate, between 50 nanometers and 500 nanometers and may be made ofan inorganic material like silicon oxide or silicon nitride or a stackof these (for example, silicon oxide-silicon nitride-silicon oxide) oran organic material like polyimide or parylene.

The hydrophobic character of the surface 14 causes the first fluid 11 toadhere preferentially to the insulating layer 13, since the first fluidhas a higher wettability with respect to the surface of the insulatinglayer 13 than the second fluid 12. Wettability relates to the relativeaffinity of a fluid for the surface of a solid. Wettability may bemeasured by the contact angle between the fluid and the surface of thesolid. The contact angle is determined by the difference in surfacetension between the fluid and the solid at the fluid-solid boundary. Forexample, a high difference in surface tension can indicate hydrophobicproperties.

Each display element 2 includes a first electrode 17 as part of thesupport plate 5. In examples shown there is one such electrode 17 perelement. The electrode 17 is electrically insulated from the first andsecond fluids by the insulating layer 13; electrodes of neighboringdisplay elements are separated by a non-conducting layer. In someexamples, further layers may be arranged between the insulating layer 13and the electrode 17. The electrode 17 can be of any desired shape orform. The electrode 17 of a display element is supplied with voltagesignals by a signal line 18, schematically indicated in the FIG.

The support plate 6 includes a second electrode 19, which may extendbetween walls of a display element or extend uninterruptedly over aplurality of display elements 2, as shown in the FIG. The electrode 19is in electrical contact with the conductive second fluid 12 and iscommon to all display elements. The electrode may be made of for examplethe transparent conductive material indium tin oxide (ITO). A secondsignal line 20 is connected to the electrode 19. Alternatively, theelectrode may be arranged at a border of the support plates, where it isin electrical contact with the second fluid. This electrode may becommon to all elements, when they are fluidly interconnected by andshare the second fluid, uninterrupted by walls. The display element 2can be controlled by a voltage V applied between the signal lines 18 and20. The signal line 18 can be coupled to a matrix of control lines onthe substrate 7. The signal line 20 is coupled to a display drivingsystem.

The first fluid 11 in this example is confined to one display element bywalls 21 that follow the cross-section of the display element. Thecross-section of a display element may have any shape; when the displayelements are arranged in a matrix form, the cross-section is usuallysquare or rectangular. Although the walls are shown as structuresprotruding from the insulating layer 13, they may instead be a surfacelayer of the support plate that repels the first fluid, such as ahydrophilic or less hydrophobic layer. The walls may extend from thefirst to the second support plate but may instead extend partly from thefirst support plate to the second support plate as shown in FIG. 1. Theextent of the display element, indicated by the dashed lines 3 and 4, isdefined by the center of the walls 21. The area of the surface 14between the walls of a display element, indicated by the dashed lines 22and 23, is called the display area 24, over which a display effectoccurs. The display effect depends on an extent that the first andsecond fluids adjoin the surface defined by the display area, independence on the magnitude of the applied voltage V described above.The magnitude of the applied voltage V therefore determines theconfiguration of the first and second fluids within the electrowettingelement. In other words, the display effect depends on the configurationof the first and second fluid in the display element, whichconfiguration depends on the magnitude of the voltage applied to theelectrodes of the display element. The display effect gives rise to adisplay state of the display element for an observer looking at thedisplay device. When switching the electrowetting element from one fluidconfiguration to a different fluid configuration the extent of secondfluid adjoining the display area surface may increase or decrease, withthe extent of first fluid adjoining the display area surface decreasingor increasing, respectively.

FIG. 2 shows a matrix of rectangular picture elements in a plan view ofthe hydrophobic surface 14 of the first support plate. The extent of thecentral picture element in FIG. 2, corresponding to the dashed lines 3and 4 in FIG. 1, is indicated by the dashed line 26. Line 27 indicatesthe inner border of a wall; the line is also the edge of the displayarea 23.

When a zero or substantially zero voltage is applied between theelectrodes 17 and 19, i.e. when the electrowetting element is in an offstate, the first fluid 11 forms a layer between the walls 21, as shownin the FIG. 1. Application of a voltage will contract the first fluid,for example against a wall as shown by the dashed shape 25 in FIG. 1 orFIG. 2. The controllable shape of the first fluid, in dependence on themagnitude of applied voltage, is used to operate the picture element asa light valve, providing a display effect over the display area 23. Forexample, switching the fluids to increase adjoinment of the second fluidwith the display area may increase the brightness of the display effectprovided by the element.

This display effect determines the display state an observer will seewhen looking towards the viewing side of the display device. The displaystate can be from black to white with any intermediate grey state; in acolor display device, the display state may also include color.

FIG. 3 shows schematically part of an example method of manufacturing anelectrowetting display device. For clarity of description, apparatusused in the manufacturing process is described in conjunction with themethod provided by the apparatus for manufacturing the device. Howeverit is to be appreciated that this description includes a description ofthe apparatus separately, i.e. when not in use and without the presenceof the materials and components of the display device being assembled tomanufacture the device. FIG. 7 is a flow diagram showing parts of anexample manufacturing process described herein.

Apparatus for providing a method of manufacturing an electrowettingdevice according to examples described herein includes a first supportplate feeding system configured to provide a first support plate and asecond support plate feeding system configured to provide a secondsupport plate.

In the examples to be described, the first support plate and the secondsupport plate for manufacturing a display device are each providedseparately from each other and are at least partially pre-assembled. So,in examples described herein, the support plate fed by the first supportplate feeding system may be the first support plate as described abovewith reference to FIG. 1 and the support plate fed by the second supportplate feeding system may be the second support plate as described abovewith reference to FIG. 2. For clarity of illustration, in FIGS. 3 to 6the first and second support plates are each shown schematically as asingle layer, without showing separate layers forming the plates. Forexample, the walls of the first support plate are not illustrated,though it is to be appreciated that they are present when the firstsupport plate is being fed through apparatus described below.

For some examples of manufacture described herein, the method may bereferred to as a “roll to roll” technique involving feeding of the firstand second support plates through the manufacturing process using aseries of rollers. Accordingly, each of the first and second supportplates to be fed through the manufacturing apparatus needs to besufficiently flexible to be manipulated by the rollers without causingthe plates damage. Thus, as explained above, the substrate in suchexamples is sufficiently flexible to bend around at least part of aroller, for being fed during the roll to roll technique. Suchflexibility applies also to other parts of the first and second supportplates, including the insulating layer, the barrier layer, the wallmaterial and the electrode described previously, such that the first andsecond support plates are sufficiently flexible to co-operate with therollers in the roll to roll technique. The flexibility of the supportplate is however limited where appropriate such that a manufacturedelectrowetting display device is sufficiently rigid for its intendedpurpose; therefore in some examples the support plates may besubstantially rigid but with sufficient flexibility for their use in theroll to roll technique when exposed to mechanical forces used during theroll to roll technique; in other examples, where the display device isintended to be flexible, the first and second support plates may be lessrigid. In examples, the materials from which the first and secondsupport plates are made are chemically and mechanically compatible withthe rollers such that there is no slip between each of the first andsecond support plates and respective rollers. Each of the first andsecond support plates may be fed respectively from a source, for examplea roll of the first support plate and a roll of the second supportplate, or in other examples each of the first and second support platesmay be fed from an earlier stage of the manufacturing process where thefirst and second support plates were at least partly manufactured.Feeding of the first and second support plates is shown in FIG. 3 byarrows F1, F2 respectively.

The first and second support plates fed by the first and second feedingsystems, respectively, may each be part of a larger sheet of a pluralityof first support plates and second support plates, respectively. Inother words, a sheet, otherwise referred to as a foil, fed by the firstsupport plate feeding system, may be dividable into a plurality of firstsupport plates after assembly of the display device, for example using a“scribe and break” process known to the skilled person. This may be donesimilarly for the second support plate. Using such a foil gives a moreefficient manufacturing process so that numerous display devices may beassembled continuously and efficiently.

In this example the first support plate feeding system includes a firstroller 30 and the second support plate feeding system includes a secondroller 32 although in other examples different elements may be usedinstead of either of the first and second rollers, for example elementswith an at least partly curved surface, to position the first and secondsupport plates relative to each other for the manufacture process to bedescribed.

The first support plate is wrapped at least partly around the firstroller, passing from a first support plate source. The second supportplate is wrapped at least partly around the second roller, after passingfrom a second support plate source. More specifically in this example anouter surface of each of the first and second support plates is wrappedat least partly around the respective first and second rollers. Thefirst roller and the second roller are separated from each other andpositioned relatively to each other such that the first support plateand second support plate are angled relatively to each other, i.e. thesecond support plate is angled relative to the first support plate andvice versa, to define, i.e. form, a cavity 34 between the first andsecond support plates. The cavity 34 narrows towards a constriction Cbetween the first and second support plates. In this example theconstriction is formed at a region between the first and second rollers30, 32 where the first and second rollers are closest to each other,i.e. a narrowest region of the cavity between the rollers, which may beotherwise referred to as a nip between the rollers. The constriction inthis example is shown in FIG. 3 between the arrows labelled C1 and C2.In this example the cavity 34 is substantially V-shaped; in other wordsthe cavity between the first and second support plates tapers or narrowstowards the constriction. A wider part of the cavity 34 above theconstriction is formed between parts of the first and second rollerswhich are less close together than at the constriction. SubstantiallyV-shaped includes shapes of the cavity 34 which have substantially flatsides, i.e. in some examples where flexible first and second supportplates are pulled taut whilst being fed between rollers and in otherexamples despite there being non-flat walls on the first support plateand in other examples which do not have flat sides, for example wheresides of the cavity 34 are curved due to a curved surface of each of thefirst and second rollers. For example, a first angle of the firstsupport plate relative to the second support plate may be greater at afirst position with a first distance between the first and secondsupport plates than a second angle of the first support plate relativeto the second support plate at a second position, at the constriction,between the first and second support plates. The first positioncorresponds with a wider part of the cavity and the second positioncorresponds with a narrower part of the cavity. With the first anglebeing greater than the second angle, the first and second support platesare in examples less parallel relative to each other at the firstposition compared with at the second position. Indeed, at the secondposition, at the constriction, parts of the first and second supportplates may be substantially parallel to each other, i.e. parallel withinacceptable manufacturing tolerances.

For manufacturing the display device, the cavity 34 is at least partlyfilled with the second fluid 12 (the second fluid 12 being shown in FIG.3 with shading). The second fluid may be provided in the cavity by asuitable second fluid supply system. The cavity 34 therefore functionsas a reservoir of the second fluid for dispensing the second fluidbetween the first and second support plates. In other words, the cavity34 functions as a container or funnel for the second fluid, with sidesof the container or funnel being formed by the first support plate andthe second support plate, from which container or funnel the secondfluid may flow. This avoids the need to submerge support plates in abath of the second fluid, as is done in known methods, to dispense thesecond fluid between the first and second support plates. Such knownmethods require considerably more second fluid than is needed to bedispensed between the first and second support plates, which can lead toinefficiencies in the manufacturing process, for example by requiringlarge volumes of possibly expensive fluids and leading to wasting orcontamination of undispensed fluid and loss due to evaporation. In thenew method of manufacture described in examples herein, using the firstand second support plates to form the second fluid reservoir, so thatthere is no need to provide the second fluid on both sides of the firstand/or second support plate for dispensing the second fluid between thefirst and second support plates, gives a more efficient method by forexample reducing at least one of the inefficiencies described above.

It is noted that a volume of second fluid in the cavity need not beenclosed on all sides to be suitably contained to form the reservoir. Infact, in examples it is sufficient to use the first and second supportplates to form the cavity; no barriers for example are required whichlie in a plane parallel to the plane that FIG. 3 is drawn in. Despitethis, in such examples, the second fluid is contained within the cavitydue to surface tension forces of the second fluid, provided that adistance between the first and second support plates in forming thecavity does not exceed a distance at which the surface tension forcesare overcome, which would cause the second fluid to spill out of thecavity. Thus, in examples, the distance between the first and secondsupport plates may be within a capillary length property of the secondfluid when interfacing with a gas surrounding an exterior of the firstand second support plates. As will be explained later, the first fluidmay be dispensed using a channel. In examples, due to the surfacetension forces of the second fluid which keep the second fluid withinthe cavity, the second fluid may also form a barrier of second fluidaround the volume of first fluid in the channel, thereby preventingfirst fluid from spilling out of the cavity.

In examples the constriction may be provided at the lowest region of thecavity 34 to assist dispensing of the second fluid between the first andsecond support plates using gravity. Indeed, in such examples, theweight of the second fluid above the constriction can help applypressure at the constriction to dispense and assist flow of the secondfluid through the constriction.

To manufacture the display device the first support plate is fed andtherefore moved over the first roller, in this example assisted byrotating the first roller in a first rotational direction R1, which inthis example is clockwise, whilst moving the first support plate overthe first roller. The second support plate is fed and therefore movedover the second roller, in this example assisted by rotating the secondroller in a second rotational direction R2, which in this example isopposite the first rotational direction and is therefore anti-clockwise,whilst moving the second support plate over the second roller.

Given the positioning of the first and second rollers, moving the firstsupport plate over the first roller and moving the second support plateover the second roller, in this example by rotating the rollers in thedirections described, moves the first and second support plates towardsthe constriction and towards each other. In other words the first andsecond support plates are brought towards each other at theconstriction. It is to be understood that in other examples the firstsupport plate may be considered to be moved towards the second supportplate whilst moving the first and second support plates towards theconstriction, or vice versa.

At the constriction the first and second support plates are broughttogether with, in this example, a distance D1 between the two supportplates which is substantially equal to a distance between the first andsecond support plates of the manufactured display device, thus settingthe distance between the plates. Thus, after having been fed through theconstriction, the distance between the first and second support platesis also substantially equal to the distance between the first and secondsupport plates of the manufactured display device. The phrase“substantially equal” covers variations from the distance of themanufactured display device due to for example variations withinacceptable manufacturing tolerances or a contraction of a sealingmaterial (described later) due to curing. The distance D1 in thisexample is taken in a direction perpendicular to a surface of the secondsupport plate adjoined by the second fluid.

Thus, at the constriction, the second fluid is dispensed between thefirst and second support plates, from the reservoir of second fluid inthe cavity 34, as a consequence of moving the first and second supportplates towards the constriction, which brings the first and secondsupport plates closer together, i.e. towards each other. Thus, duringdispensing the first and second support plates are moved through theconstriction and the second fluid is dispensed from the reservoir,through the constriction, to in-between the first and second supportplates. As the second fluid is dispensed, it may in some examples benecessary to supply more of the second fluid into the cavity 34, using asuitable second fluid supply system, to maintain a supply of secondfluid for dispensing at the constriction whilst continuing to feed thefirst and second support plates. Further, supplying more of the secondfluid may be necessary to maintain a channel of the first fluiddescribed below. In other examples, the volume of the second fluidprovided in the cavity may be sufficient for dispensing the second fluidfor an intended duration of dispensing the second fluid. Dispensing ofthe second fluid may in examples be controlled in dependence on a rateof rotating the first and second rollers; therefore an appropriate ratemay be chosen to ensure a satisfactory and stable flow of the secondfluid.

The first fluid is dispensed on at least one part of a surface of thefirst support plate. In this example, the first fluid is dispensed onthe surface of the display area of each display element of the firstsupport plate. This is illustrated in FIG. 3 as regions of the firstfluid 11. It is to be appreciated that the first fluid is dispensed onthe surface of further display areas of the first support plate notillustrated; these include display areas of further of the sheet to befed to the constriction but also further display areas across an extentof the first support plate taken in a plane perpendicular to the planeof the FIG. It is to be noted that although the walls of displayelements are not illustrated in FIG. 3, for clarity, they are indicatedin FIG. 3 with the label 21 where there is an interruption betweenregions of first fluid 11.

To dispense the first fluid, the first fluid is provided in part of thecavity 34 between the first and second support plates using for examplea first fluid supply system. More specifically, the first fluid isprovided at least partly, in this example entirely, within a channel 36formed between a part 38 of a surface of the first support plate and thesecond fluid 12. The channel may have the form of a longitudinaldepression in the second fluid, a groove, a trough or a longitudinalrecess. The channel of first fluid is formed due to the immiscibility ofthe first and second fluids and therefore an interface, i.e. meniscus,between the first and second fluids defines, i.e. determines, a form ofthe channel. A sufficient volume of first fluid is supplied adjacent tothe first support plate, on a surface of the second fluid in the cavity34, to form the channel of first fluid. Therefore, the channel of firstfluid functions as a reservoir of first fluid for dispensing the firstfluid on the surface of the first support plate. Given the hydrophobicproperties of the display areas of the first support plate, the firstfluid rather than the second fluid tends to wet the display areas. Thus,as the first support plate is moved towards the constriction, in thisexample by moving the first support plate over the first roller, thepart 38 of the surface of the first support plate is moved along a sideof the channel 38 and the display areas are wet by the first fluid. Asthe first support plate continues to be moved towards the constriction,the display areas remain coated with the first fluid, these beingdispensed regions of first fluid for the manufactured display device.FIG. 3 shows a region of first fluid being formed as an extruded regionof first fluid extending along the surface of the first support platefrom the channel 38. As the walls are less hydrophobic than the displayareas and are therefore less wettable to the first fluid than to thesecond fluid, being for example hydrophilic, the walls are not coatedwith the first fluid given the preference of the first fluid to wet thedisplay areas. Dispensing of the first fluid, for example the thicknessof the first fluid layer formed on each display area, may be controlledby controlling one or more of the following: the angle of the firstsupport plate, a speed of moving the part 38 of the surface of the firstsupport plate along the side of the channel, in this example the speedof feeding the first support plate over the first roller; the volume offirst fluid in the channel; the volume of the second fluid in thecavity; or the properties of the first fluid such as the wettability ofthe first fluid for the display areas. In some examples it may benecessary to supply more of the first fluid in the channel duringdispensing of the first fluid on the surface of the first support plate,using a first fluid supply system, to maintain a supply of the firstfluid in the channel; in other examples the volume of first fluid in thechannel may be sufficient for the intended duration of dispensing thefirst fluid. In examples, as the skilled person will understand, theshape of the channel may be controlled using one or more of: controllinga shape of the channel using one or more of: a position of the furthersurface relative to the part of the surface of the first support plate;a spacing between the further surface and the part of the surface of thefirst support plate, a wettability of the further surface for the firstfluid, a wettability of the further surface for the second fluid, avolume of the provided second fluid, a volume of the provided firstfluid, a surface tension property of the first fluid, a surface tensionproperty of the second fluid, an extent of immiscibility of the firstand second fluids, a density of the first fluid, a density of the secondfluid, a shape of the interface between the first and second fluids, ashape of the further surface, or an angle of the part of the surface ofthe first support plate relative to the further surface.

In examples a sealing material for coupling the first support plate withthe second support plate is dispensed on a surface of a part of thesecond support plate before that part of the second support platereaches the constriction during moving the first and second supportplates towards the constriction. Although for clarity the sealingmaterial is not shown in FIG. 3, a sealing material dispensing system 40for dispensing the sealing material is illustrated. The sealing materialin examples is for forming a sealing element for sealing a perimeter ofa display device and which therefore may be formed as a rectangular orsquare shaped seal for example for surrounding a matrix of displayelements of the display device being manufactured. Therefore, thesealing material may be dispensed with a suitable shape and ofsufficient thickness for coupling the first and second support plates atthe constriction. The sealing material is dispensed in this examplebefore the constriction and feeding the second support plate moves thesealing material towards the constriction C. At the constriction C wherethe first and second support plates are closest together, the firstsupport plate is coupled with the second support plate by bringing thefirst support plate into contact with the sealing material dispensed onthe part of the surface of the second support plate. The dispensing ofthe sealing material may be timed in coordination with the speed ofrotating the first and second rollers and in dependence on a layout ofdisplay areas of the first support plate, including for example asealing region (not illustrated) of the first support plate which lacksdisplay areas and which surrounds a matrix of display areas for thedisplay device, so that the first support plate is coupled with thesecond support plate at the desired location, i.e. the sealing region.The sealing material may be dispensed as a curable and mouldablecompound such that, when dispensed with a thickness greater than thedistance D1, the constriction applies pressure to the sealing materialvia the first and second support plates, thereby compressing the sealingmaterial between the first and second support plates to ensure suitableadhesion of the sealing material to each of the first and second supportplates, to provide a suitable seal for the display device. With thesealing material being curable, the sealing material may be irradiated(not illustrated) with ultraviolet light after the constriction to curethe sealing material and thereby form the sealing element. In otherexamples the sealing material may be a pressure sensitive adhesive.

After the sealing material has been cured to form the sealing elementand with the support plates having been fed through the constriction,the assembled display device is fed in the direction F3 to be processedfurther, for example to divide the coupled first and second supportplate sheets to form individual display devices.

FIG. 4 illustrates a different example of part of a method ofmanufacturing an electrowetting display device. Features of theapparatus and their role in manufacturing the display device are similarto those described using FIG. 3 and are labelled in FIG. 4 using thesame reference numbers; corresponding descriptions apply. Differences inthe example of FIG. 4 compared with that of FIG. 3 will therefore bedescribed.

In this example of FIG. 4 a dispensing of the first fluid on the displayareas of the first support plate is performed differently than in FIG.3. A further surface is provided in this example by a further elementwhich in this example is a third roller 42 positioned relative to andspaced from the first support plate 5 to form a second constriction 44in this example between the arrows labelled C3 and C4. The secondconstriction is formed between the first support plate and a surface ofthe third roller 42 before a first support plate is fed to theconstriction C. A tension in the first support plate, between the firstroller 30 and not illustrated parts of the first support plate feedingsystem located before the first roller, maintain a position of a part ofthe first support plate relative to the surface of the third roller 42,thereby defining, i.e. forming, the second constriction where the thirdroller is closest to a surface of the first support plate. The thirdroller 42 is positioned to be at least partly immersed in the secondfluid in the cavity 34 between the first and second support plates.First fluid is supplied in a cavity 46 between part of the first supportplate and the third roller. A channel 48 is formed between a part of thesurface of the first support plate, the second fluid 12 in the cavity 34between the first and second support plates and the surface of the thirdroller. As for the channel described previously, the channel 48 isformed due to the immiscibility of the first and second fluids andtherefore an interface, i.e. meniscus, between the first and secondfluids defines, i.e. determines, a form of the channel 48. The form ofthe channel is influenced too by the position of the surface of thethird roller 42 and therefore by the second constriction 44. The firstfluid is dispensed on the display areas of the first support plate by,and therefore at, the second constriction 44, as the first support plateis moved towards the constriction C by the first roller 30. Morespecifically, the part of the surface of the first support plate formingthe channel 48 is moved along a side of the channel 48. The secondconstriction 44, specifically a size of a spacing between the furthersurface and the part of the surface of the first support plate, controlsa thickness of the first fluid for dispensing the first fluid, thethickness in this example being taken in a direction perpendicular tothe surface of the part of the first support plate at the secondconstriction 48. For example, the second constriction 44 reduces athickness of the first fluid and aids spreading of the first fluidacross a surface of the first support plate for being coated by thefirst fluid. Factors described above for controlling dispensing thefirst fluid with reference to FIG. 3 apply appropriately in this exampletoo.

In this example, first fluid 50 is supplied on the surface 52 of thethird roller 42 using a fourth roller 54. The fourth roller ispositioned relative to the third roller to provide a third constriction56 between the third and fourth rollers, the third constriction beingindicated by the arrows C5 and C6. First fluid is provided at the thirdconstriction 56, for example by a first fluid supply system. The thirdconstriction controls an amount of first fluid supplied on the surfaceof the third roller to form a layer and therefore an amount of firstfluid provided by the third roller in the channel 48 between the thirdroller and the first support plate. The third roller is rotated in thisexample in an anticlockwise rotational direction R3 to provide firstfluid in the channel 48, with in this example the fourth roller beingrotated in an opposite rotational direction R4, i.e. clockwise in thisexample, to control providing of first fluid on the third roller, i.e.transferring of first fluid from the fourth roller to the third rollersurface. The third roller may be rotated during the moving the part ofthe surface of the first support plate along the side of the channel Aspeed of rotating the third roller, relative to the speed of the movingthe part of the surface of the first support plate along the side of thechannel, in examples controls a rate of dispensing the first fluid onthe part of the surface of the first support plate.

In this example of FIG. 4 the second roller 32 performs the function ofthe second roller described using FIG. 3 but has a larger diameter thanthe first roller in this example, to form a deeper cavity 34. Thus thecavity 34, when filled with second fluid 12, immerses part of the thirdroller, for forming the channel 48.

Although walls of the first support plate are not illustrated, it is tobe appreciated that the second constriction 44 is sized such that thewalls of the first support plate may be fed through the secondconstriction 44 without damage. The third roller may therefore bepositioned so as not to contact the walls as the first support plate isfed through the second constriction 44. Further, in examples, the wallsmay have poor wettability for the first fluid, meaning that first fluidfrom the channel 48 may not be deposited on the walls; any first fluidwhich might be applied to the walls is skimmed off the walls by thefirst fluid in the channel of first fluid, thus further aiding accuratedispensing of the first fluid on the display areas.

FIG. 5 illustrates schematically another example of part of amanufacturing method of an electrowetting display device. Features ofthe apparatus and their role in manufacturing the display device aresimilar to those described using FIG. 3 and are labelled in FIG. 5 usingthe same references numbers; corresponding descriptions apply.Differences in the example of FIG. 5 compared with that of FIG. 3 willtherefore be described.

In this example of FIG. 5, further features are described which aredifferent compared with the example of FIG. 3 but which havesimilarities to those described previously. Such features are labelledwith the suffix “a” and take a similar description as given previously,but with differences now described.

In this example the second support plate 58 has a different constructionthan described previously and instead has in this example a similarconstruction to that of the first support plate. A further first fluidis provided in a further part of the cavity and within a further channel36 a formed between a part 60 of a surface of the second support plateand the second fluid 12. The further first fluid may have the samecomposition as the first fluid 11 described previously or may bedifferent, for example coloured with a different dye than the firstfluid dispensed on the surface of the first support plate using thechannel 36. The further first fluid is dispensed on the part 60 of thesurface of the second support plate by moving the second support platetowards the constriction C, as described previously, which moves thepart 60 of the surface of the second support plate along a side of thefurther channel 60, for dispensing the further first fluid as regions 11a of the further first fluid on display areas of the second supportplate.

In the example of FIG. 5 a further support plate 62 is provided, forexample from a further support plate feeding system, as shown by arrowF4. The further support plate feeding system is configured to providethe further support plate angled relative to the second support plate todefine, i.e. form, a further cavity 64 between the second support plate58 and the further support plate 62. In this example the further supportplate has a similar construction as the first support plate 5. Thefurther cavity is formed between a surface of the second support plate58 furthest away from the display area of the second support plate. Thefurther cavity 64 narrows towards a further constriction 66, indicatedbetween arrows C7 and C8, formed between the second support plate andthe further support plate provided on a further roller 68 of the furthersupport plate feeding system which roller is positioned for forming thefurther constriction. The further cavity 64 is at least partly filledwith a further second fluid 12 a which may be the same chemicalcomposition as the second fluid 12 described previously or of adifferent composition. The further second fluid in the further cavity 64therefore provides a further reservoir of the further second fluid fordispensing the further second fluid between the second support plate andthe further support plate.

In this example the further support plate 62 is moved over a furtherelement, in this example the further roller 68 which the further supportplate is at least partly wrapped around. The further roller 68 functionsin a similar way as the first roller, by moving the further supportplate towards the further constriction 66 and towards the second supportplate for dispensing the further second fluid at the secondconstriction, assisted by rotating R5 the further roller. In otherexamples, the second support plate may be moved towards the furthersupport plate or both the second and further support plates may be movedtowards each other.

A further first fluid 72, which may be the same or of a differentcomposition than the first fluid described previously, is provided inpart of the further cavity 64 and within a further channel 70. Thefurther channel 70 is formed between a part of the surface of thefurther support plate and the further second fluid, although in otherexamples the further channel may be formed between the second fluid anda part of the surface of the second support plate. The further channelfunctions in a similar manner as the channel 36 described using FIG. 3and that description should be taken to apply here, for dispensing thefurther first fluid by moving the appropriate one of the second supportplate and the further support plate along a side of the further channel,to provide regions of the further first fluid 72 on display areas of thefurther support plate. A further first fluid supply system may be usedfor supplying the further first fluid in part of the further cavity toform and maintain the further channel of the further first fluid. Areservoir of the further second fluid in part of the further cavity maybe formed and maintained using a further second fluid supply system (notillustrated) for supplying further second fluid into the further cavity.Further rollers may be used to assist supplying of the further firstfluid as described similarly for supply of the first fluid using FIG. 4.

The second support plate and the further support plate are coupledtogether in this example in a similar way as coupling the first andsecond support plates described previously, using a further sealingmaterial dispensing system 40 a for dispensing a further sealingmaterial on a surface of a part of the further support plate beforereaching the further constriction during moving the second and furthersupport plates towards the constriction, with the second and furthersupport plates being coupled together by bringing the second and furthersupport plates together, so the second support plate contacts thefurther sealing material; the previous description should be taken toapply here, modified accordingly.

FIG. 6 illustrates schematically a different example of part of amanufacturing method of an electrowetting display device. Features ofthe apparatus and their role in manufacturing the display device aresimilar to those described using FIG. 3 and are labelled in FIG. 6 usingthe same reference numbers; corresponding descriptions apply.Differences in the example of FIG. 6 compared with that of FIG. 3 willtherefore be described.

In this example, a first support plate 74 is fed F1 to and over thefirst roller 30, by wrapping the first support plate at least partlyaround the first roller. In this example the first support plate has aconstruction similar to the second support plate described using FIG. 3.A further support plate 76, also similar in construction to the secondsupport plate of FIG. 3, is fed F4 from an appropriate feeding system.In this example the further support plate is fed to and over the secondroller 32, by for example wrapping the further support plate at leastpartly around the second roller. A second support plate 78, which inthis example is similar in construction to the first support plate 5described using FIG. 3 but in this example may be comprised of a singlesubstrate 7 with a stack of the electrode, barrier layer, hydrophobiclayer and walls formed on two opposite and parallel surfaces of thesubstrate 7. The second support plate is fed F2 between the first andthe further support plates 74, 76 using an appropriate feeding system.The first and second rollers 30, 32 are positioned separate from andrelative to each other to form a constriction between the first andsecond rollers as indicated by arrows C1 and C2. However, in thisexample, in contrast with that of FIG. 3, the constriction includes twoconstrictions; a constriction 80 between the first and second supportplates and a constriction 82, which may be referred to as a furtherconstriction, between the second and further support plates.

The first support plate is angled relative to the second support plateand the further support plate is angled relative to the second supportplate, to provide, respectively, a cavity 84 between the first supportplate and the second support plate and a cavity 86 between the secondsupport plate and the further support plate. These cavities are at leastpartly filled with a second fluid, which may be the same or differentfor each cavity 84, 86. In a similar manner as described previously,rotating the first and second rollers moves the first and furthersupport plates over the first and second rollers respectively; also inthis example by feeding the second support plate 78 appropriately,second fluid is dispensed by the constrictions 80, 82, respectivelybetween the first and second support plates and between the second andfurther support plates, by moving at least one of the first and secondsupport plates and at least one of the second and further support platestowards each other, to bring them together.

A channel 88, 90 of a first fluid is formed in each of the cavities 84,86. The channels 88, 90 are each similar to the channel describedpreviously using FIG. 3 except being formed respectively between thesecond fluid in each cavity and part of the second support plate. Thefirst fluid is dispensed by moving the second support plate along theside of each channel 88, 90. The first fluid in each channel may be thesame or different for each cavity 84, 86. With a similar first fluiddispensing method as described above, regions of first fluid 92 may beformed on display areas of the second support plate.

The above embodiments are to be understood as illustrative examples. Theexample of FIG. 5 is an example of manufacturing a display device withthree layers of first fluid each for example coloured differently,whereas the example of FIG. 6 is an alternative method of manufacturinga display device with two layers of first fluid. It is to be appreciatedthat further types of display device may be manufactured using theprinciples described above, for example using a cavity between twosupport plates as a second fluid reservoir and for example using achannel of first fluid for dispensing the first fluid. In some suchexamples, a support plate may be used having a different constructionthan described above; for example, a support plate with a constructionmore similar to that of the first support plate described above withFIG. 1 may be used rather than the second support plate described withFIG. 1 and vice versa.

In the example described using FIG. 4, a third roller and a fourthroller are used as part of a process for dispensing the first fluid. Itis envisaged that in further examples the use of at least a surface,such as of a roller, may be used in the manner of using the third rollerand optionally the fourth roller to dispense a first fluid on a supportplate of an electrowetting device; in some examples such a first fluiddispensing technique may be used without dispensing the second fluid inthe manner described above. In other words, these methods of dispensingthe first and second fluids may be used independently of each other, infurther examples. Therefore, in further examples, with reference to FIG.8, a method of manufacturing an electrowetting display device comprises:providing a first support plate; providing the first fluid and thesecond fluid, the first fluid being provided at least partly within achannel formed by: a part of a surface of the first support plate, aninterface between the first fluid and the second fluid, and a furthersurface; the first fluid is dispensed on the part of the surface of thefirst support plate by moving the part of the surface of the firstsupport plate along a side of the channel. In some such examples, thesecond fluid may be provided as a reservoir of second fluid contained bya container such as a bath, with the first support plate being immersedin the bath of second fluid, rather than the second fluid reservoirbeing provided in a cavity between the first and second support plates,as described in examples above. In some examples, the first supportplate is provided such that the part of the surface of the first supportplate and a horizontal plane forms an angle of one of: between 90degrees and 170 degrees or between 135 and 160 degrees. In accordancewith some such further examples, apparatus may be used which comprises afirst support plate feeding system configured to provide the firstsupport plate having a surface; a system for providing a reservoir ofthe second fluid; and a further surface for example as described above,for forming a channel within which the first fluid is at least partlyprovided. As explained in examples above, the channel may be formed by:a part of the surface of the first support plate, an interface betweenfirst fluid in the channel and the second fluid, and the furthersurface. The first support plate feeding system in such examples isfurther configured to move the part of the surface of the first supportplate along a side of the channel, to dispense the first fluid on thepart of the surface of the first support plate.

Examples described above relate to electrowetting display devices.Further examples are envisaged for manufacturing an electrowettingdevice which is not a display device.

Further examples are envisaged. It is to be understood that any featuredescribed in relation to any one embodiment may be used alone, or incombination with other features described, and may also be used incombination with one or more features of any other of the embodiments,or any combination of any other of the embodiments. Furthermore,equivalents and modifications not described above may also be employedwithout departing from the scope of the accompanying claims.

What is claimed is:
 1. An apparatus for manufacture of an electrowettingdevice comprising a first fluid and a second fluid, the apparatuscomprising: a first support plate feeding system configured to provide afirst support plate during the manufacture of the electrowetting device;a second support plate feeding system configured to provide a secondsupport plate during the manufacture of the electrowetting device, thefirst support plate feeding system comprising a first element and thesecond support plate feeding system comprising a second element, thefirst element and the second element positioned relative to each otherso as to angle the first support plate relative to the second supportplate such that the first support plate and the second support plate arebrought closer together as the first support plate and the secondsupport plate are fed by the first element and the second element,respectively, so as to provide, during the manufacture of theelectrowetting device, a cavity between the first support plate and thesecond support plate; a first fluid supply system configured to supplythe first fluid, during the manufacture of the electrowetting device, tothe cavity; and a second fluid supply system configured to supply thesecond fluid, during the manufacture of the electrowetting device, tothe cavity.
 2. The apparatus of claim 1, wherein: the first fluid supplysystem is configured to supply the first fluid, during the manufactureof the electrowetting device, in a first part of the cavity; and thesecond fluid supply system is configured to supply the second fluid,during the manufacture of the electrowetting device, in a second part ofthe cavity different from the first part of the cavity.
 3. The apparatusof claim 1, wherein the first fluid supply system is configured tosupply, during the manufacture of the electrowetting device, the firstfluid in at least one of: a first channel between: a first surface ofthe first support plate; and the second fluid; or a second channelbetween: a second surface of the second support plate; and the secondfluid.
 4. The apparatus of claim 1, wherein the first fluid supplysystem is configured to dispense, during the manufacture of theelectrowetting device, the first fluid on at least one of: a firstsurface of the first support plate or a second surface of the secondsupport plate.
 5. The apparatus of claim 1, wherein the second fluidsupply system is configured to provide, during the manufacture of theelectrowetting device, a reservoir of the second fluid in the cavity. 6.The apparatus of claim 1, wherein: the first element comprises a firstroller; and the second element comprises a second roller, the firstroller rotatable to move, during the manufacture of the electrowettingdevice, the first support plate towards the second support plate and thesecond roller rotatable to move, during the manufacture of theelectrowetting device, the second support plate towards the firstsupport plate, to bring the first support plate and the second supportplate closer together.
 7. The apparatus of claim 6, wherein the firstroller has a first diameter and the second roller has a second diameter,the first diameter smaller than the second diameter.
 8. The apparatus ofclaim 1, wherein the first fluid supply system comprises a third elementwith a third element surface, the third element positioned such that,during the manufacture of the electrowetting device, there is: a thirdchannel between: a first surface of the first support plate, a secondfluid surface of the second fluid, and the third element surface.
 9. Theapparatus of claim 8, wherein the third element comprises a third rollerrotatable, during the manufacture of the electrowetting device, toprovide the first fluid in the third channel.
 10. The apparatus of claim9, wherein the first fluid supply system is configured to supply thefirst fluid between the third roller and a fourth roller.
 11. Theapparatus of claim 1, comprising a sealing material supply systemconfigured to supply, during the manufacture of the electrowettingdevice, a sealing material onto a second surface of the second supportplate.
 12. The apparatus of claim 1, wherein: the first fluid issubstantially electrically non-conductive; and the second fluid is atleast one of electrically conductive or polar.
 13. The apparatus ofclaim 1, comprising a third support plate feeding system configured toprovide, during the manufacture of the electrowetting device, a thirdsupport plate angled relative to the second support plate such that thethird support plate and the second support plate are brought closertogether as the third support plate is fed by the third support platefeeding system, so as to provide a second cavity between the secondsupport plate and the third support plate.
 14. The apparatus of claim13, wherein the third support plate feeding system comprises a fifthroller rotatable to move, during the manufacture of the electrowettingdevice, the third support plate towards the second support plate, tobring the second support plate and the third support plate closertogether.
 15. The apparatus of claim 13, comprising: a further firstfluid supply system configured to supply a further first fluid duringthe manufacture of the electrowetting device; and a further second fluidsupply system configured to supply a further second fluid during themanufacture of the electrowetting device.
 16. The apparatus of claim 15,wherein: the further first fluid supply system is configured to supplythe further first fluid, during the manufacture of the electrowettingdevice, in a further first part of the second cavity; and the furthersecond fluid supply system is configured to supply the further secondfluid, during the manufacture of the electrowetting device, in a furthersecond part of the second cavity different from the further first partof the second cavity.
 17. The apparatus of claim 13, comprising afurther first fluid supply system configured to supply a further firstfluid, during the manufacture of the electrowetting device, in at leastone of: a further first channel between: a second surface of the secondsupport plate; and a further second fluid; or a further second channelbetween: a third surface of the third support plate; and the furthersecond fluid.
 18. The apparatus of claim 13, comprising a further firstfluid supply system configured to dispense, during the manufacture ofthe electrowetting device, a further first fluid on at least one of: asecond surface of the second support plate or a third surface of thethird support plate.
 19. The apparatus of claim 13, comprising a furthersecond fluid supply system configured to supply a further second fluidduring the manufacture of the electrowetting device, the further secondfluid supply system configured to provide, during the manufacture of theelectrowetting device, a reservoir of the further second fluid betweenthe second support plate and the third support plate.
 20. The apparatusof claim 13, wherein the second support plate feeding system isconfigured to provide, during the manufacture of the electrowettingdevice, the second support plate at least partly between the firstsupport plate and the third support plate.